1. Field of the Invention
Embodiments of the present invention generally relate to apparatus and methods for compressing and communicating a visual image from a host computer to a remote computer. More specifically, a dynamic color index table is deployed at a host computer to compress sections of the visual image by transforming pixel values to indexed color value approximations which are encoded and communicated.
2. Description of the Related Art
Color image quantization is the process of constructing a reduced color palette for a wide color-range image (e.g., 24-bit color) to represent the color image in a reduced color range (e.g., 8-bit color) for purposes such as supporting low-cost color display or printing devices of reduced capabilities or multimedia compression. Sometimes, such image quantization is used in conjunction with half-toning or dithering techniques, such as error diffusion, to reduce contouring effects and improve the visual quality of the quantized image.
In some cases, such a reduced color palette is determined ahead of time independent of the particular image being encoded. For example, in the case of the 3-3-2 palette popular in wireless applications, 3 bits of color information are used for the red and green channels of an image while 2 bits of color information are used for the blue channel of the image to produce 256 different color values using an 8-bit representation. In other cases, the image is analyzed and a palette selected and ordered to meet image quality, color accuracy, and/or compression objectives.
Some bitmap-oriented image file formats, such as the Graphics Interchange Format (GIF) or Portable Network Graphics (PNG), use color quantization in conjunction with lossless index compression to provide image file size scaling and portability in applications such as the web browsers. However, none of these methods meet the objectives of enabling fast lightweight compression while also maintaining high image quality. These objectives are necessary for software-based compression of high frame rate synthetic image streams as may be encountered in remote display applications.
Therefore, there is a need in the art for a system and method for enabling fast lightweight compression of image streams to provide improved image quality over conventional color image quantization techniques.